During processing of semiconductor substrates that are to contain integrated circuits and/or heads of disk drives (such as read and write heads), it is common to planarize a wafer by use of chemical mechanical polishing (CMP). Typical chemical mechanical polishing (CMP) systems use a polishing arm and carrier assembly 110 (FIG. 1A) that press the top surface of a semiconductor wafer 101 against a rotating polishing pad 102 mounted on a platen 120.
Post-CMP within wafer non-uniformity (WIWNU) could depend on many factors such as incoming wafer film uniformity, down force, wafer curvature back-side-pressure (BSP), wafer to retaining ring protrusion, retaining ring pressure, pad, conditioning, table and carrier speed, slurry distribution, oscillation, etc. However, inventors note that the effect from back-side-pressure (BSP) on post-CMP uniformity is much more significant than other parameters. We found that Post CMP wafer uniformity is dominated by polishing BSP.
Bow (convex) is the typical global geometry of wafer deformation due to the wafer substrate bow and film stress. The compressive stress from deposition processing causes convex bending. Based on the incoming wafer and process maps, the back-side-pressure in the process recipe can be adjusted to bend wafer by positive, vacuum, or radical zone back-side-pressure and optimized to obtain polishing uniformity or compensate for film center-to-edge thick or thin incoming film thickness. Back-side-pressure can push the back of a wafer and accelerate the center polishing rate for center-thick-edge-thin film or center-slow-edge-fast process. It also can vacuum the back of the wafer and decrease the center polishing rate for the center-fast-edge-slow process.